The subject matter disclosed herein relates generally to electric machines. More specifically, the subject disclosure relates to torsional dampers for electric machines.
Historically, electrical power generation for ground vehicles has been accomplished via an alternator driven by a pulley connected to an engine crank shaft. As vehicle electric power demands increase, the ability of pulley-driven alternators to carry the mechanical loads from the crank shaft to the generator becomes limiting. As an alternative to a pulley-driven alternator, the electrical generator may be installed directly in the driveline of the engine. By installing the generator in the driveline, there are no pulley, gear, or chain systems needed to transfer load from the generator to the engine and/or power from the engine to the generator.
In a typical ground vehicle driveline, rapidly fluctuating torque output of the engine is smoothed through the use of a flywheel. The flywheel does not, however, entirely remove cyclic speed variations of the engine's output shaft. To further smooth the torque output of the engine, other means such as torsional dampers or fluid dynamic couplings are installed between the transmission and the engine. Installation of the generator in the driveline further compounded the issues because when coupled to the engine crank shaft, the generator's rotational inertia increased torsional stresses on the crank shaft leading to failure of the crank shaft. To alleviate this issue, a torsional damper, typically a long shaft, is installed between the generator and the engine flywheel. To decrease the overall length of the driveline generator installation, a more compact torsional damper is desired.